1. Technical Field
The present invention relates to wireless communication and, more particularly, to a method and apparatus for transmitting a feedback request and a method and apparatus for receiving a feedback request in a wireless communication system.
2. Related Art
IEEE (Institute of Electrical and Electronics Engineers) 802.16e standards have been adapted in the name of ‘WMAN-OFDMA TDD’ as sixth standards for IMT (International Mobile Telecommunication)-2000 in ITU (International Telecommunication Union) affiliated ITU-R (ITU-Radio communication sector) in 2007. ITU-R is preparing an IMT-Advanced system as next-generation 4G mobile communication standards after IMT-2000. IEEE 802.16 WG (Working Group) has determined to promote an 802.16m project to aim at creating amendment standards of the existing IEEE 802.16e, as standards for the IMT-Advanced system in late 2006. As noted from the aim, 802.16m standards involve the continuity of the past 802.16e standards and the continuity of the futuristic next-generation IMT-Advanced system. Thus, 802.16m standards are required to satisfy the advanced requirements for the IMT-Advanced system while maintaining the compatibility with the 802.16e standard-based Mobile WiMAX system.
A MIMO (Multiple Input Multiple Output) may be considered as a technique for supporting a reliable high speed data service. The MIMO technique improves data transmission and reception efficiency by using multiple transmission antennas and multiple reception antennas. The MIMO technique includes spatial multiplexing, transmit diversity, beamforming, or the like. A MIMO channel matrix according to the number of reception antennas and transmission antennas can be disassembled into a plurality of independent channels. Each independent channel is called layer or stream. The number of layers is called rank.
A user equipment (UE) may transmit feedback through uplink. The feedback may include channel information required for a data transmission. A base station (BS) may schedule radio resources by using the feedback received from the UE, and transmit data. A closed loop scheme is transmitting data by compensating for channel information included in the feedback from the UE, and an open loop scheme is transmitting data without compensating for channel information included in the feedback from the UE. The feedback may not be transmitted in the open loop scheme, and if ever, the BS may not use the channel information included in the feedback. In general, in a wireless communication system, the open loop scheme may be applied in a channel environment for a UE moving at a high speed, and the closed loop scheme may be applied in a channel environment for a UE moving at a low speed. Because the channel for the UE moving at a high speed severely changes, channel information included in feedback is not reliable, so the open loop scheme is employed. The channel environment for the UE moving at a low speed does not greatly change relatively, so the channel information included in feedback is reliable and less vulnerable to delay, so the closed loop scheme can be employed.
The BS transmits a feedback request, and the UE transmits appropriate feedback information to the BS by using control information included in the feedback request. For example, in IEEE 802.16, the BS transmits a feedback request called feedback polling A-MAP IE. Such a feedback request is generally transmitted by a limited number of bits. However, it may happen that the conventional feedback polling A-MAP IE stipulated in IEEE 802.16 may include a number of bits exceeding the limited number of bits.
Thus, a method and apparatus for reducing overhead without exceeding the limited number of bits when the BS transmits a feedback request are required.